The 24-year-old Sunit shared second place with Chandigarh's Karandeep Kochhar, the winner of the last TATA Steel PGTI event at Tollygunge Club in 2016, as well as Bengaluru's Syed Saqib Ahmed and Bangladesh's Badal Hossain.
Karan, playing only his third event as a professional after making the grade from the 2019 PGTI Qualifying School, reaped the dividends for his brilliant putting on Tuesday as he drained an eagle and four birdie putts from a range of 10-20 feet.
Karan, who plays at the DLF Golf iamp; Country Club in Gurugram, was quick off the blocks with birdies on his first three holes. He added another on the eighth before sinking a 15-footer for eagle on the par-5 13th.
The six-footer, who finished tied 16th at the PGTI Q School earlier this year to earn a full card on the tour, finally picked up two more shots on the 14th and 18th to make it the most memorable day of his fledgling professional career.
Karan, who was among India's leading juniors till the age of 15, said, "I hardly missed a fairway today and that's the key to playing well at this course. While my hitting was spot-on, my putting was even better. I also did well with the wedges, especially the gap-wedge and didn't make any errors.
"The three birdies at the start just took my confidence to another level. It was also great to end the round with a 12-foot birdie conversion on the 18th."
Chowrasia, fresh from a career-best seventh place finish at the PGTI Players Championship at Classic Golf iamp; Country Club last month, continued his hot form as he put together an eagle, six birdies and a bogey for a 63 in round one. He chipped-in from 13 yards for his eagle on the 13th.
Karandeep Kochhar, who as an amateur at age 17 became the youngest player to win during the last PGTI event at Tollygunge Club in 2016, once again enjoyed himself at his happy hunting ground with a 63 that featured an eagle, seven birdies and two bogeys. He was eight-under through 10 holes before slowing down with a bogey on 11 and all pars thereafter.
Syed Saqib Ahmed's hot putter earned him five birdie conversions from a range of 10-20 feet. He finished in style by nearly finding the hole with his tee shot on the par-3 18th. He tapped-in for birdie there and, therefore, also shared second place at 63.
Badal Hossain's round, which included an eagle, six birdies and a lone bogey also bunched him in the four-way tie for second place at 63.
Among the prominent names, Order of Merit leader Rashid Khan of Delhi was in tied 12th at 65, while Bengaluru-based Rahil Gangjee was a further shot back in tied 15th at his original home course.
Local favourite SSP Chawrasia shot a 69 to be tied 45th even as another Kolkata-bred Bengaluru-based player Viraj Madappa occupied tied 66th place after a round of 71.